I think part of the disconnect is also that you both wanted different things. You want an exclusive relationship and he doesn’t. Hopefully, you’ll meet another man soon, and he will also want the same as you.
When you saw he was flirting with other women, both times you dated, you knew he wasn’t interested in being exclusive. It’s about boundaries. Rather than standing by, you put on the brakes when you see he’s not giving you what you want.